Before diving into the following technical charts, you should probably know that understanding all this is not actually necessary to know if you are getting a good deal on a diamond. There are really only TWO things overall a consumer needs to know

The complete "Grading" of the diamond you are looking at or desire.This "Grading" will include generally 4 things.

First and foremost Clarity (amount of imperfections)

The Carat (weight)

Color(D-M) to (D-Z)

Cut (which has to do with the symmetry and light reflectivity (brilliance)

Who graded the diamond

There are very high standards in this area so if the diamond is "certified" by a reputable association like GIA, etc, this is optimal and can be trusted.

If it was privately appraised or graded by a trained and credentialed diamond expert, these gradings can also be trusted to a lesser degree depending on the reputation and skill of said appraiser.

You should probably stay away from diamonds not professionally graded.

Once you know these two things, you should be able to shop around and see if the diamond you are looking at is a good value because diamonds with the exact same grades should be close in prices. (I say close because there are other characteristics that effect the desirability of a diamond such as florescence and inclusion placement which can have an impact on price although less significant).

Example - A GIA graded SI1 1.01 carat G color with excellent cut should be more expensive than a privately graded diamond that is the same.

THE 4 C's OF BUYING A DIAMOND

CUT

Most often a person gets confused and thinks cut is the shape of the diamond but actually it refers to the angles and proportions of a diamond. Diamond cut is considered the most important of the four Cs, so it is important to understand how it affects the properties and values of a diamond. Diamonds that are cut either too deep or too shallow can lose or leak light through the sides and bottom and will be less brilliant-and ultimately of less value. But a well cut diamond is able to handle light better, creating more scintillation and more sparkle which leads to brilliance.

CLARITY

Diamonds are graded for clarity under 10x loupe magnification. Clarity ranges from flawless (perfect) to I (included). Below is the chart that certification societies have standardized for grading to describe the clarity of a diamond.

F - Flawless: No internal or external flaws. Extremely rare.

IF - Internally Flawless: no internal flaws, but may have minor flaws on the outside. Very rare.

VVS1-VVS2 - Very, Very Slight Inclusions: Have very small inclusions. It's very difficult to detect inclusions under 10 x magnifications even by a trained gemologist. VVS1 inclusions can only be seen through the pavilion. VVS2 inclusions are more visible.

VS1-VS2 - Very Slightly Included: Inclusions can only be seen with difficulty under 10x magnification. VS1 inclusions are harder to see than VS2.

SI1-SI2 - Slightly Included: Inclusions easy to see under 10X magnification and might be visible to the naked eye

I1-I2-I3 - Included: Inclusions visible to the human eye.

COLOR

Diamond's color is usually referring to the presence or absence of color in white diamonds. Diamonds act as prisms and can divide light into a spectrum of colors and reflect this light as colorful flashes referred to as fire. The more colorless a diamond is the more colorful the fire will appear.Diamond colors generally range from D - Z for white and yellow diamonds. D is the whitest. Around S they become "Fancy" yellow Diamonds.

CARAT - WEIGHT

This is the weight of a diamond measured in carats. One carat is equivalent to 200 milligrams. Sometimes one carat is referred to as 100 "points", so that a diamond of 75 points weighs .75 carats. Carat-weight is the easiest of the 4C's to determine. But two diamonds of equal weight can have very unequal value, depending on their cut, color and clarity. Larger diamonds often cost more per carat due to their size. Diamond cost increases exponentially with an increase in weight because larger diamonds are rarer than smaller diamonds and this rarity increases the value of a larger diamond.